Circuit breaker



April 25, 1961 2,981,811

H. M. STEVEN ET AL CIRCUIT BREAKER 5 Sheets-Sheet 1 Filed Aug. 22, 1957 INVENTORS HARRY M. STEVEN,

RAYMOND \Al- MARSHALL BYWMQL- CW7 ATTORNEY April 1961 H. M. STEVEN EI'AL 2,981,811

CIRCUIT BREAKER Filed Aug. 22, 1957 5 Sheets-Sheet 2 INVENTORS HARRY M. STEVEN, RAYMOND \M MARSHALL QMj A TTORNEY April 1961 H. M. STEVEN ETAL 2,981,811

CIRCUIT BREAKER 1 M w ""1 M W i 1p 777777 W P Miami INVENTORS 6| HARRY M. STEVEN, r RAYMOND W MARSHALL 3'5 fia M-Tfi $417 A T'TGRNEY P 1961 H. M. STEVEN ETAL 2,981,811

cmcun BREAKER Filed Aug 22, 1957 5 Sheets-Sheet 4 INSULATION INVENTORS HARRY M. STEVEN, RAYMOND W. MARSHALL ka M12- A T'TORNE Y April 1961 H. M. STEVEN ETAL 2,981,811

CIRCUIT BREAKER 5 Sheets-Sheet 5 Filed Aug. 22, 1957 INVENTORS HARRY M. STEVEN, RAYMOND W- MARSHALL A TIORNEY United States Patent CIRCUIT BREAKER Harry M. Steven, Schenectady, and Raymond Marshall, Scotia, N.Y., assignors to General Electric Company, a corporation of New York Filed Aug. 22, 1957, Ser. No. 679,606

7 Claims. (Cl. 200-88) Our invention relates to electric circuit breakers and especially to circuit breakers including a main insulating housing and a trip unit enclosed in a separate housing removably mounted in the main insulating housing.

Prior circuit breakers of the type referred to have ordinarily included a trip unit having a latch projecting therefrom which restrains an element of the circuit breaker mechanism from moving to tripped position. Release of the latched element involves a sliding motion between the two parts. Such sliding friction is likely to be inconsistent and unpredictable, making such circuit breakers difficult to calibrate. It also causes wear on latch surfaces increasing the likelihood of changes in calibration.

In addition, prior art circuit breakers have incorporated trip units which, following initial installation, repair or change of the trip unit, cannot be tested for mechanical operativeness except by actually causing high overload currents to flow therethrough. This is usually inconvenient, and often impossible to do at the time of such installation, repair or replacement.

Circuit breakers incorporating removable trip units have, in the past, presented certain dif'ficulies in initial manufacture, in connection with adjustment and calibration. Such trip units usually incorporate two currentresponsive devices for each pole, and various mechanical linkages for relating these devices all to a single releasable latched element. Usually the calibration process has to be repeated several times before a sufficiently accurate adjustment is achieved. This is largely because certain factors involving manufacturing tolerances and fitting of parts cannot be computed beforehand but must be compensated for by trial and error.

It is an object of our invention to provide an electric circuit breaker including a removable trip unit having a restraining latch which utilizes pivoting rather than sliding friction.

It is another object of our invention to provide a circuit breaker incorporating a removable trip unit which includes a test button which can be used to mechanically operate the trip unit when installed in the breaker in the same manner that the unit would be operated by electric current action.

Another object of the invention is to provide an improved circuit breaker trip unit having a plurality of adjusting means whereby accurate preliminary adjustments can be made, thereby simplifying and accelerating the calibration process.

Another object of our invention is to provide an electric circuit breaker trip unit incorporating a magnetic field piece for use at high current values which can be formed by molding techniques, rather than requiring assembly of stamped metallic laminations, thereby reducing cost.

In accordance with our invention, we provide an electric circuit breaker including a main insulating enclosure and a separately enclosed trip unit rigidly mounted in the main enclosure. A latch member projects from the 2,981,811 Patented Apr. 25, 1961 ICC trip unit and is adapted to engage a member of the circuit breaker operating mechanism normally to restrain it from causing automatic opening or tripping of the circuit breaker. The projecting latch member comprises a pivotally supported member which is biased in a releasing direction when the circuit breaker is in the "on" condition. The latch member is normally restrained from moving in a tripping direction by a pair of toggle links, mounted in an upwardly overset condition and acting as a collapsible bracing strut for the latch member. Current responsive means is also provided, which is arranged to exert a force on the toggle to move the knee downwardiy to cause it to collapse and to release the circuit breaker trip member when certain overload currents occur.

Additional objects of our invention will be pointed out in the following detailed description and illustrated in the accompanying drawings, and the scope of our invention will be particularly pointed out in the appended claims.

In the drawings,

Figure l is a side elevation view partly in section, of an electric circuit breaker incorporating our invention;

Figure 2 is a perspective view of a circuit breaker trip unit constructed in accordance with our invention;

Figure 3 is a side elevation view of a portion of the tripping mechanism of the circuit breaker trip unit of Figure 1;

Figure 4 is a fragmentary view of a portion of the mechanism of Figure 2 with the bimetallic strip shown in a heated or deflected condition;

Figure 5 is a sectional view taken along the lines 5-5 of Figure 7;

Figure 6 is a sectional elevation view taken along the lines 66 of Figure 7;

Figure 7 is a side elevation view of the trip unit of Figure 2;

Figure 8 is a sectional view of a portion of the trip unit, taken generally on the line 8-8 of Figure 7;

Figure 9 is an exploded view of the interior parts of the circuit breaker trip unit of Figure 2, the magnet and armature being omitted from one pole;

Figure 10 is an exploded view in perspective of a portion of a circuit breaker incorporating our invention and showing particularly the cover member for covering the trip unit adjusting levers and the terminals or lugs;

Figure 11 is a perspective view of the magnet utilized in the circuit breaker trip unit of Figure 1, and

Figure 12 is a perspective view of a modified magnet for use in the circuit breaker trip unit of Figure 1.

In the drawings, we have shown our invention as embodied in a three-pole electric circuit breaker comprising an outer or main insulating casing having a base 10 and a cover 11. Mounted on the base 10 at one end thereof are three load terminals 12 (only one shown) and, at the opposite end of the base 10, three line terminals 13 (only one shown). The line terminals 13 are each connected to a line contact strap 14, and each strap 14 carries a pair of side-by-side stationary main contacts 15 (only one shown) and a single stationary arcing contact 16, forming a triangular configuration of contacts for each pole.

The main and arcing contacts 15 and 16 of each pole cooperate with corresponding pair of movable main contacts 17 and a movable arcing contact 18, respectively. Each of the three movable contacts of each pole is independently movable and is pivotally supported on a common pivot pin 19' carried by the contact arm 19 and each is biased away from the contact arm 19 by one of the contact pressure springs 17' and 18'. The contact arm 19 is pivotally supported in the base 10 upon a pivotal axis 20. The movable arcing contact member 18 of each pole has most of its weight forward of the pivot pin 19'. The movable main contacts each has most of its weight to the rear of the pivot pin 19'. The effect of this is that the inertia of the contacts thereby causes the main contacts to open first and the arcing contact to open last, which is the desired sequence. The movable contacts 17 and 18 of each pole are connected by means of multistrand flexible bra'ds 21 to one terminal 22 of the trip unit 23 and the load terminal 24 of the trip unit 23 is connected directly to the main load terminal 12 of the circuit breaker.

For the purpose of moving the movable contacts 17 and 18 into and out of engagement with the stationary or line contacts and 16, both manually and automatically, we provide a main operating mechanism indicated generally at 25. The operating mechanism shown is more particularly shown and described in application Serial Number 679,607, filed August 22, 1957, by E. B. Judd and J. D. Young, and assigned to the same assignee as the present invention, now issued as Patent No. 2,921,169, January 12, 1960, and will be only briefly described herein.

The operating mechanism shown includes a generally U-shaped supporting frame member 26 and a plurality of parts pivotally supported between the opposite sides thereof. These parts include three contact arms 19 (only one shown), there being one contact arm for each pole of the circuit breaker. The contact arms 19 are adapted to be rotated about their pivotal support by means of a toggle action linkage including the toggle links 27 and 28, connected together at a toggle knee point 29 and supported at their upper end on a pivot pin 30 carried by a toggle carrier 31. The toggle links 27 and 28 are adapted to be operated between straightened and collapsed positions by means of an operating handle 32 in cooperation with a pair of tens'on type springs 33 interconnected between the handle 32 and the knee point 29 of the toggle linkage 27, 28. When the handle member 32 is in the position shown in Figure l, the contacts are in closed position and when the handle is moved counterclockwise from this position toward the left end of the breaker as viewed, the contacts are moved to the open circuit position. The end of the toggle carrier 31 is formed to act as a latching element and to engage an intermediate latch member 34 which is pivotally and slidably supported on a pin 35 carried by the frame 26. The action of the tension springs 33 is such as to bias the toggle carrier 31 for rotation in a clockwise direction. The toggle carrier 31 is restrained from movement in such a direction however by its engagement with the intermediate latch member 34. A biasing spring, 34', constantly urges the intermediate latch 34 in a clockwise direction as viewed in Figure 3. By reason of the greater force exerted on it by the toggle carrier 31, however, the intermediate latch member 34 is biased in a counterclockwise direction when the breaker is latched. It will be observed that intermediate latch 34 constitutes a releasable trip member which, upon a predetermined amount of movement in counterclockwise directfon as viewed in Figure 3, causes automatic opening of the movable contacts of the circuit breaker. As will be described in greater detail hereafter, member 34 is engaged and restrained by the trip unit latch member to retain the breaker in its normal operating condition.

For the purpose of normally restraining the intermediate latch member 34 and therefore the toggle carrier 31 and the operating mechanism as a whole in the on position except in the case of predetermined overload conditions, we provide a trip unit generally indicated at 23.

The trip unit 23 includes an insulating housing, to be more fully described, and a latch member '36 adapted normally to prevent the intermediate latch member 34 from rotating in a. counterclockwise direction. The latch member 36 is pivotally supported on the trip unit 23 on a pivot pin 37, extending through aligned openings in a boss 38 molded integral with the housing of the trip unit 23.

The latch member 36 carries a latch roller 39 supported on a pin 40 extending between opposed, spaced apart, portions of the latch member 36. The intermediate latch member 34 is provided with a cam surface 41 which, when the breaker is latched, bears against the roller 39 and biases the latch member 36 in a counterclockwise direction, that is, to the left as viewed in Figure 3. It will be observed that since the intermediate latch 34 is carried by the main breaker frame, by far the greater portion of the force required to hold the toggle carrier 31 in latched condition is taken by the main breaker frame, and not by the trip unit mounting. In addition, the intermediate latch reverses the direction of force of the carr'er 31 and the force exerted on the latch 36. Therefore the trip unit 23 is acted upon by forces acting in a downwardly direction, thus putting no great strain on the trip unit or its mounting.

The latch member 36 is prevented from moving to the left by the action of a pair of toggle links 42 and 43 which are interconnected between a relatively stationary pivot pin 44 carried by the trip unit 23 and the pivot pin 40 carried by the latch member 36. The toggle links 42 and 43 are interconnected and joined by a knee pivot pin 45. The toggle linkage including the links 42 and 43, is biased in an upwardly or overset direction by means of a spring 46 which surrounds a portion of the pin 40 and has its opposite ends engaging the toggle link 42 and the latch member 36 respectively. The bias of the spring 46 is such as to urge the knee pivot pin 45 upwardly as viewed in Figure 3, tending to cause collapse upwardly of the toggle linkage 42, 43 and therefore movement of the latch member 36 counterclockwise as viewed in this Figure 3.

Movement of the knee of the toggle linkage 42, 43 upwardly is limited by its engagement with a toggle adjusting screw 47 carried by an integral boss 48 on the trip bar 49. The trip bar 49 is, in turn, prevented from rotating in a counterclockwise direction by its engagement with a trip bar adjusting screw 50. The parts are therefore retained normally in the condition shown in Figure 3 and in Figure 1.

The trip bar 49 is pivotally supported in the trip unit housing on an axis coaxial with the pin 44. Clockwise rotation of the trip bar 49 by the current responsive means in a manner to be described causes the toggle adjusting screw 47 to move the knee of the toggle to and through the dead center position until the toggle collapses downwardly. At the same time, the latch 36 moves to the left, carrying the latch roller 39, and allowing the intermediate latch member 34 to rotate counterclockwise and to release the carrier 31, with consequent opening of the contacts.

Following such release, the intermediate latch is urged clockwise by its bias spring 34, against a stop portion 26' of the frame 26. This permits the trip toggle 42-43 to reset itself due to the action of the bias spring 46, these parts returning, after cooling of the bimetallic strip, substantially to the condition of Figure 3.

In order to relatch the breaker following a tripping operation, the handle 32 is moved manually to the left to and slightly beyond the normal off position. During this movement, a portion 32' of the handle engages the carrier 31 and rotates it counterclockwise. When the latch tip of the carrier 31 engages the surface 348 of the intermediate latch 34, further counterclockwise movement of the carrier causes the intermediate latch 34 to move to the left, as viewed, with a combined pivoting and sliding action, as permitted by the elongated pivot notch 34N. The ends of the bias spring 34 also are adapted to slide along the inner surface of the portion 345 to permit this sliding retracting action. The latch tip of the carrier 31 finally clears the latch surface of the intermediate latch, and the intermediate latch is returned to its normal position by the action of the spring 34', thereby relatching the breaker.

The trip bar 49 is adapted to be rotated by means of a thermally responsive trip device and a magnetically responsive trip device in a clockwise direction, as viewed, to cause tripping or automatic opening of the circuit breaker. The thermally responsive trip device includes a bimetallic strip member 51 fixedly mounted at one end on the terminal portion 22, and carrying an adjustable calibrating screw 52 at its opposite end. In order to prevent accidental alteration of the calibration such as by vibration, the calibrating screw is mounted in a lock-nut device 53 which is, in turn, carried by the bimetallic strip 51.

In order to heat the bimetallic strip 51 in accordance with current passing through the circuit breaker, an intermediate reduced portion 54 of the conductor is provided between the terminals 22 and 24 comprising a heater portion. As will be observed from Figure 9, the heater portion 54 is of reduced cross section thereby increasing the resistance of this portion of the conductor and concentrating the heating therein. Current does not pass through the bimetallic strip member. instead, the bimetallic member is mounted closely adjacent and preferably against the heater portion 54 of the conductor. The terminals 22 and 24, together with the intermediate heater portion 54, comprise a single continuous conductor 56 of relatively rigid non-laminated material. The terminal portions 22 and 24 are therefore adapted to serve as mounting supports for the trip unit, and, since they are relatively heavy and inflexible, are adapted to prevent any movement or misalignment of the trip unit with respect to the circuit breaker mechanism which might cause a change in calibration of the breaker.

Magnetic or instantaneous tripping action is provided by means of a relatively stationary magnet 55 surrounding the conductor 56 and mounted on the trip unit housing by suitable means such as by screws 57. The magnet 55 is generally U-shaped and surrounds the heater portion 54, whereby the current passing through the heater portion also serves to create a magnetic field in the magnet 55. Magnetic armatures 58 are provided, one for each pole, pivotally supported with respect to the magnet member, on the same pivotal axis as the trip bar 49. Each of the armatures 58 includes upwardly bent portions 58' having aligned holes therein adapted to receive one of the pivot pins 44.

Upon the occurrence of excessive overloads or short circuit currents, the magnet 55 attracts the armature 58 causing it to strike a projection on the trip bar 49, rotating the trip bar 49 clockwise, collapsing the toggle linkage and tripping the circuit breaker.

The armature 58 is biased at all times in a counterclockwise direction against an adjustable stop screw 59. For this purpose, a tension spring 60 is provided having one end thereof connected to the armature 58 at the upwardly bent portions 58, and the other end connected to an adjusting lever 61. The adjusting lever 61 is pivotally supported in an open-ended recess or notch in the trip unit housing, being held there by the bias of the spring 60. As the adjusting lever 61 is moved from its upper to its lower position, as indicated in Figure 6, the line of action of the adjusting spring 60 is moved closer to the pivot point of the armature 58 and vice versa. This changes the efiective bias of the spring 60 on the magnetic armature and varies the amount of current required to cause magnetic actuation.

A flat spring member 62 is attached to the lever 61 and has its outer end return-bent. This provides a rounded cam surface adapted to ride against the cam surfaces 63 formed in the trip unit housing. The action of this spring 62 in moving over the cam surfaces 63 affords a step-by-step adjusting action for the lever 61.

Adjustment of the maximum and minimum magnetic tripping values is achieved by an adjustable mounting of the spring 60 on the lever 61. This adjustable mounting includes a short mounting lever 64 pivoted on the lever 61 at 65, and carrying the end of the spring 60 at its outer end. The mounting lever 64 also has an oliset portion 66 which bears against an adjusting screw 67 carried by the main adjusting lever 61. As the adjusting screw 67 is turned inwardly, the lever 64 is rotated clockwise as viewed in Figure 6, stretching the tension spring 60, and increasing the bias on the magnetic armature 58. Thus the length of the spring 60 is varied without moving the lever 61.

Certain aspects of the magnetic tripping apparatus disclosed herein form a part of the subject matter disclosed and claimed in our application Serial Number 679,590, filed concurrently herewith and assigned to the same assignee as the present invention and now issued as Patent No. 2,884,497, April 28, 1959.

The trip unit housing includes two mating molded parts 68 and 68, the part 68 being larger and serving as a base for supporting the various parts of the trip mechanism. The part 68 serves as a cover and also supports some of the parts. The two portions 68 and 68 of the trip unit 23 are adapted to be fastened together by suitable means such as by bolts and nuts 88, arranged to be insulated and made effectively non-removable by filling over the ends thereof with a suitable material such as a potting compound or cement. Other fastening means such as spun-over tubular rivets may of course be used instead of bolts.

The trip unit casing part 68 includes an arcuate boss 69 for each pole of the circuit breaker, each arcuate boss having an elongated slot 70 through which the outer portion of the adjusting lever 61 projects. Each slot 70 also preferably includes a shield portion 71 at right angles to the general direction of the adjusting lever 61, the adjusting lever 61 having an offset integral portion 72 passing through the slot. Each of the slots 70 therefore does not afford a direct opening to the interior of the trip unit.

Initial assembly of the adjusting lever 61 into the slot 70 is accomplished by providing each slot 70 with a portion 73 at one end wherein the shield 71 is omitted to admit the outer end of the adjusting lever 61 including the ofiset portion 72.

The conductor 56 is fastened rigidly to the base portion of the trip unit housing by suitable means such as by screws 74 and 75.

In order to enclose the adjusting means for the armatures 58 without unduly enlarging the trip unit housing, the cover member 68 is provided with projecting portions or chambers 76 at corresponding points.

Each of the magnets 55 preferably has two auxiliary pole members 77, each comprising an elongated strip of magnetic material projecting beyond the pole faces of the magnet 55 and having its outward end upwardly bent to extend closely adjacent to the armatures 58 when they are in their unattracted position. The auxiliary pole members 77 maintain a relatively small backward pull on the armatures 58 during normal currents and minor overload currents. On the occurrence of relatively large over-currents, however, the intermediate portions of the auxiliary pole member 77 become saturated and the pull of the main pole portions of the magnet 55 greatly exceeds the backward pull of the auxiliary poles 77. The net etfect of this action is to cause the armatures 58 to move to closed position with what may be termed a snap" action. The auxiliary pole members 77 may be and preferably are, omitted in forms of the invention used for lower ampere rated circuits, such for instance as -300 amperes.

The trip unit housing members 68 and 68 have matching cut-away portions which provide openings or windows in the top wall thereof adapted to permit access to the adjusting screws 67. Following adjustment of the screws 67, the apertures are closed by relatively thin fiber insulating members 78, which are snapped" in place, being trapped therein under tapered ledge retaining portions 78'. The trip unit base 68 also has apertures 79 which are aligned with calibrating screws 52, and through which the calibrating screws 52 may be adjusted from outside the unit casing after the casing is completely assembled.

In order to facilitate testing of the mechanical operation of the trip unit when installed in a circuit breaker, means is provided for tripping the trip unit manually when desired. For this purpose, a plunger 80 is mounted in a recess in the trip unit base 68 and has a reduced portion extending thru the trip unit wall, with the inner end adjacent the trip bar 49. A biasing spring 80', under the head of the plunger 80, biases it outwardly away from the trip bar, outward travel being limited by a retaining clip or washer on the inner end of the plunger. An inward force on the plunger 80 against the force of a bias spring 80, causes the inner end of the plunger to engage the trip bar 49 rotating it in a tripping direction.

The trip unit cover 68' supports the parts relating to the tripping toggle and also supports a bracket member 81 adapted to interengage with a portion 82 of the side frames 26 of the mechanism proper, to prevent any relative movement between the two members.

The major portion of one end wall of the main outer enclosure 10 is omitted, and a depending barrier 11' is provided. The remaining end opening is closed by the trip unit housing when the trip unit is in assembled position, as shown in Figures 1 and 10. As indicated in these figures, when the breaker is completely assembled and the trip unit is in place, the adjusting levers 61 for each of the poles of the circuit breaker are readily accessible for operation from outside the circuit breaker, although the trip unit itself is inaccessible and cannot be removed without removal of the top cover 11.

The circuit breaker is adapted to be mounted on a suitable support by suitable mounting means such as by bolts (not shown) which are available through the mounting holes 83.

For the purpose of normally preventing ready access to the adjusting levers 61, as well as accidental contact with the terminals 12 or access to the mounting holes 83, we provide a generally S-shaped molded insulating cover member 84 removably attached to the circuit breaker cover 11 by suitable means such as by screws 85. When the insulating cover 84 is removed, it is possible to mount the circuit breaker or attach it to a suitable support to electrically connect it by means of the lugs 12, and to adjust the magnetic trip members by means of the levers 61. When the insulating cover 84 is in assembled position however, access to all of these elements is prevented.

The magnet member 55 is preferably formed with a central core 55A of relatively solid magnetic material and outer layers 55B of laminated magnetic material. By means of this construction, it is possible to drill and tap mounting holes in the back wall of the magnet to facilitate mounting thereof on the insulating housing of the trip unit.

In Figure 11 we have shown a modified form of the magnet 55 in which the magnet 55' is formed of magnetic powder material bonded together by a suitable plastic resin. This type of magnet field piece has high electrical resistance, thereby reducing eddy-current heating to a minimum, and has been found to be highly suitable for use in high ampere rated circuit breakers. Such a magnet can be readily produced by conventional molding techniques thus eliminating the need for stamping lamination forms and fastening them together. In a typical application, it has been found that a satisfactory magnet field piece is provided for circuit breakers rated in the range of 250 to 600 amperes by molded bodies of the following composition:

(A) Magnetic core member suitable for use in circuit breakers rated 250-325 amperes:

64 parts by volume of iron powder, annealed low metalloid, 200 mesh 23 parts by volume of phenol-aldehyde resin Minimum density of core, 4.82 gm./ cc. (B) Magnetic core member suitable for use in circuit breakers rated 350-600 amperes:

60 parts by volume of iron powder annealed low metalloid 200 mesh 4 parts by volume of powdered mica filler, wet

ground, 200-325 mesh 23 parts by volume of phenol-aldehyde resin Minimum density, 4.62 gm./cc.

It will be observed from the above that in circuit breakers rated 250-325 amperes, a magnetic core material is used comprising approximately 25% by volume of nonmagnetic material. In breakers rated 350-600 amperes, a magnetic core material is used comprising approximately 30% by volume of non-magnetic material. Other suitable materials may of course be utilized as fillers and binders. For instance, we may use as such binder any of the following resins: Melamine-formaldehyde resins, polyester resins, silicone resins; and We may use as such filler any of the following fillers: Wood flour, asbestos, macerated fabric.

It will be observed that the trip mechanism of the trip unit 23, including the thermal and magnetic tripping elements have been provided with a number of independently manipulatable adjustments as indicated particularly in Figure 3. Adjustment and calibration of the circuit breaker is carried out using these adjustments, in the following manner. Initially, before the trip unit is mounted in the circuit breaker, all adjusting screws are retracted. With no current passing through the breaker, the armature adjusting screw 59 is turned in until the armature touches magnet 55 (closed position). The screw 59 is then retracted a predetermined small amount such as one turn, establishing a first position of the armature short of the closed position. With the parts in this condition, the toggle adjusting screw 47 is turned inwardly sufiiciently to cause the toggle links 42, 43, to move to collapsed position. This assures that when the armature has reached its first position short of closing, the trip toggle will have been broken. Following this, the screw 59 is then turned outwardly an additional predetermined amount such as 3 /2 turns to establish a desired initial air gap, set in accordance with the current at which tripping is desired. The trip bar adjusting screw 50 is then turned in sufficiently to contact the trip bar 49, thereby establishing the normal position of the trip bar. Following the preliminary adjustments, the trip unit is mounted within the circuit breaker proper and the breaker is placed in the on position. With the breaker in this condition, the trip toggle adjusting screw 47, which is accessible through the central opening in the top of the trip unit casing, is given a final adjustment. As mentioned above, a component of the main operating spring force trying to move the carrier 31 upwardly, is trans mitted, through the intermediate latch 34, to the toggle 42-43. The proportion of such force which i transmitted can be varied in a particular design in a number of ways, but most easily by varying the steepness of the latch angle" of the cam surface 41.

It will also be observed that regardless of the "latch angle, the amount of force required to force the trip toggle over-center can be varied by varying the amount of over-set of the toggle. Thus the greater the overset, the greater the force required to move the toggle back through dead center, and vice versa. We have found that the best results are obtained as to stability, uniformity of calibration and dependability, when the overset is such as to require a force of lb. to 1 lb. force on the trip bar at a point adjacent the end of the calibrating screw 52 to initiate movement and cause tripping. Following such force calibration of the toggle, the adjusting screw 52 for the thermal element 51 is adjusted in accordance with the predetermined current conditions to cause thermal tripping as desired.

As an independent adjustment, the adjusting screw 67 for the armature bias spring may be adjusted to determine the maximum and minimum amount of current required to cause magnetic tripping. By way of further adjustment, it is possible to replace the spring 60 with other springs of differing strength.

The trip unit 23 is also provided with a bracket 86 attached thereto by suitable means such as by rivets and having an intermediate portion thereof spaced away from the top wall of the trip unit to provide a convenient means for lifting the trip unit out of the circuit breaker. The bracket 86 also includes a further offset portion 86A which is adapted to extend within an opening 87 in the top wall of the circuit breaker cover 11 to provide a marking or indication of the circuit breaker current ratmg.

A trip bar 49 is provided with spaced deeply cut notches 49' extending therewithin to a point past the axial center of the pivot pins 44 for the purpose of providing clearance for the adjusting lever 61, whereby the levers 61 may move the springs 60 to a position substantially in line with the pivotal axis of the trip bar 49 when in the fully depressed condition such for instance as shown in dotted lines in Figure 6.

While we have shown one specific embodiment of our invention, it will be appreciated that many variations thereof may readily be made by those skilled in the art, and we therefore intend by the appended claims to cover all such variations as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

I. An electric circuit breaker comprising at least one pair of relatively movable contacts, operating mechanism for manually operating said relatively movable contacts between open and closed circuit positions, said operating mechanism including a movable member movable to cause automatic opening movement of said contacts, a first insulating housing enclosing said operating mechanism and said contacts, and a current responsive trip assembly including a second insulating housing removably mounted in said first insulating housing and including a pair of terminals for connecting said trip assembly in series with said contacts, said trip assembly including a latch member mounted on an external surface of said second housing normally restraining said movable member to prevent automatic opening of said contacts, said trip assembly also including a pair of interconnected toggle links extending through said wall of said second housing connected to said latch member and constructed and arranged when in straightened condition to hold said latch member in restraining position, and current responsive means for exerting a force on said toggle linkage within said second housing to cause collapse of said toggle linkage upon the occurrence of predetermined current conditions through said trip assembly and consequent release of said movable member.

2. An electric circuit breaker comprising at least one pair of relatively movable contacts, a trip member movable in a predetermined direction to cause automatic opening of said movable contacts, means biasing said trip member for movement in said predetermined direction, a latch member normally restraining said trip member from movement in said predetermined direction, said latch member including a rotatable sleeve portion adapted to engage said releasable trip member to restrain it from movement in said predetermined direction, said trip member acting on said rotatable sleeve portion so as to urge said latch member toward a releasing condition, and a pair of toggle links normally restraining said latch member from movement in said releasing direction.

3. An electric circuit breaker comprising a main inlulating enclosure, at least one pair of relatively movable contacts mounted within said insulating enclosure, operating mechanism for operating said contacts between open and closed circuit position including a manually operable handle member for moving said movable contacts between open and closed circuit positions and a member releasable to cause automatic opening of said contacts, a trip unit including a separate insulating housing mounted within said enclosure said trip unit including a member adapted to engage and normally restrain said releasable member, and a releasing button carried by said trip unit, said button being manually operable to cause actuation of said trip device and release of said releasable member.

4. An electric circuit breaker comprising at least one pair of relatively movable contacts, operating mechanism for manually operating said relatively movable contacts between open and closed circuit positions, said operating mechanism including a movable member movable to cause automatic opening of said contacts, an insulating housing enclosing said operating mechanism and said contacts, a current-responsive trip assembly removably mounted in said insulating housing and including a pair of terminals for connecting said trip assembly in series with said contacts, said trip assembly including a latch member normally restraining said movable member to prevent automatic opening of said contacts, said trip assembly also including a pair of interconnected toggle links connected to said latch member and constructed and arranged when in straightened condition to hold said latch member in restraining position, current-responsive means for exerting a force on said toggle linkage to cause collapse of said toggle linkage upon the occurrence of predetermined current conditions through said trip assembly and consequent release of said movable member, said trip assembly also including an insulating housing separable from said circuit breaker housing, and a continuous rigid conductor extending through said trip assembly housing and having its opposite ends adapted to serve as trip assembly terminals, said conductor being fixedly attached to said trip assembly housing, whereby said conductors may be used to physically mount said trip assembly within said circuit breaker housing without the need for additional fastening means.

5. An electric circuit breaker comprising a main insulating enclosure, at least one pair of relatively movable contacts mounted within said main insulating enclosure, operating mechanism including a manually operable handle member for moving said movable contacts between open and closed circuit positions and a member releasable to cause automatic opening of said contacts, a trip unit including a separate insulating housing mounted within said main enclosure, said trip unit including a latch member for engaging and normally restraining said releasable member, a trip member within said trip unit and movable to cause releasing movement of said latch member, an aperature in said trip unit housing, a plunger supported for reciprocal movement within said aperture and including a portion disposed and arranged to engage said movable member within said trip unit housing to cause movement of said trip member upon movement of said plunger inwardly of said housing 6. An electric circuit breaker comprising at least one pair of relatively movable contacts, operating mechanism for moving said contacts between open and closed circuit positions, said operating mechanism including a member movable to cause automatic opening of said contacts, means biasing said member for movement in said opening direction, latch means normally restraining said movable member from opening movement, and means for causing releasing movement of said latch means including a magnetic armature member and a magnetic core member energized in accordance with current passing through said circuit breaker, said magnetic core member com prising a homogeneous mixture of iron powder and a non-magnetic filler held together by a resinous binder, said non-magnetic filler and said resinous binder complising at least 20% by volume of said magnetic core member.

7. An electric circuit breaker as set forth in claim 6 wherein said resinous binder comprises a material selected from the class comprising melamine-formaldehyde resins, polyester resins, silicone resins and wherein said filler comprises a material selected from the class comprising wood flour, asbestos, macerated fabric.

References Cited in the file of this patent UNITED STATES PATENTS Lingal July 14, 1936 12 Runke Nov. 7, 1944 Favre Dec. 6, 1949 Leonard Aug. 10, 1954 Rosing Mar. 1, 1955 Tombs Feb. 26, 1957 Katz Feb. 26, 1957 FOREIGN PATENTS Germany Dec. 1, 1925 Germany Nov. 14, 1930 Great Britain Oct. 17, 1934 Great Britain Apr. 4, 1938 Germany July 13, 1938 Switzerland May 16, 1941 

